I'm still looking for a ticket, too.
But as I live close to Mannheim I even consider just going there and looking out for someone who is selling their ticket if Ebay won't work.

Have you checked Ebay out, yet (I mean the german one)? It is a good chance there I think.
There are still lots of tickets on sale, especially two-ticket-packages.
And they go there for reasonable prices.

http://shop.ebay.de/i.html?_from=R40...All-Categories